1. Field of the Invention
The present invention relates to a sputtering method and apparatus for forming a thin metal film on the surface of a semiconductor wafer.
2. Description of the Related Art
In general, a method is employed in which a metal called a target is sputtered and deposited on a semiconductor wafer at the time of forming electrodes or the like in the semiconductor devices. In this method, the target is disposed on a cathode electrode, while a semiconductor wafer is disposed at the position opposing this target. Sputtering energy is applied to the target in an inert gas atmosphere under a pressure of several Pascals for the purpose of sputtering the target so that it is deposited on the semiconductor wafer.
FIG. 1 shows the structure of a conventional sputtering apparatus. A target 2 and a wafer retainer 3 are disposed in an opposed manner in a sputter chamber 1 which is disposed in a housing 1a. The wafer retainer 3 is provided for the purpose of holding semiconductor wafers 12, and is disposed in such a manner that the distance from the target 2 to the wafer retainer 3 can be changed by an adjusting device 5 secured to the housing 1a. A cathode of a DC power source 4 is connected to the target 2, while an anode of the same is connected to the housing 1a. Gas sources 7a to 7d are connected to the sputter chamber 1 via corresponding valves 8a to 8d. Furthermore, the DC power source 4, the adjusting device 5 and the valves 8a to 8d are electrically connected to a controller 6 so that they are respectively controlled by this controller 6. A vacuum pumping device (not shown) is connected to the sputter chamber 1.
Next, the operation of the above-described conventional apparatus will be described while employing Ti as the target 2 and Ar in the gas sources 7a to 7d as the sputtering gas.
First, the semiconductor wafers 12 are set on the wafer retainer 3, and the internal pressure in the sputter chamber 1 is decreased by the unillustrated vacuum pumping device to provide a high vacuum state. The valve 8a is then opened by the controller 6 so that the Ar gas is supplied into the sputter chamber 1 from the gas source 7a to fill the sputter chamber 1 with an Ar gas atmosphere at a pressure of 0.5 to 2.0 Pa.
When a direct current voltage is supplied from the DC power source 4 to the target 2 in this state, a glow discharge occurs between the target 2 and the wafer retainer 3. With the glow discharge, Ar ions are generated to create a plasma. The Ar ions thus generated crash into the target 2 which is connected to the cathode of the DC power source 4, causing Ti atoms to be sputtered from the target 2. As a result of this, a thin film of Ti is deposited on the semiconductor wafers 12 held on the wafer retainer 3.
The characteristics of the Ti film which has been deposited on the semiconductor wafers 12 are determined by the pressure level of the Ar gas in the sputter chamber 1, the voltage level and the current value applied to the target 2, and the distance between the target 2 and the semiconductor wafers 12.
However, since the relationships between each of the factors have not been clarified thoroughly yet, sputtering and measuring the characteristics of the actually deposited thin Ti film are alternately conducted with each of the factors adjusted for the purpose of obtaining a thin Ti film having the required characteristics. Therefore, a great deal of time and labor are needed to obtain a thin metal film having the required characteristics.